1. Field of the Invention
The present invention relates to a spacecraft and, more particularly, to performing round-trip orbital maneuvers with a spacecraft.
2. Prior Art
A major impediment to exploitation of the economic and scientific potential provided by orbiting platforms, such as for example the International Space Station (ISS), has been the high cost of launching payloads from the Earth to the orbiting platforms. The conventional approach has generally utilized single or multi-stage expendable or partially reusable launch vehicles, such as for example the Delta, Titan, and Atlas-Centaur class of launch vehicles, or the manned Space Shuttle. These launch vehicles launch the payloads from Earth directly into the orbits of the orbiting platforms. This approach has a high cost due to the high cost of the launch vehicle itself and to the large quantity of propellant used for transporting the payload with one launcher (even if multi-staged) from the Earth""s surface to the orbiting platform above. The prior art seeks to lower launch costs by launching the payloads into an initial orbit, and then using an orbiting space tug or ferry for transferring the payloads from the initial orbit to the orbit of the orbiting platforms. Use of orbiting space tugs to ferry payloads between orbits incorporates the benefits of reusability, yet, to date, the prior art""s use of orbiting space tugs has resulted in a negligible reduction in the expected costs of launching payloads to the orbiting platform. The use of orbiting space tugs in the prior art has been limited merely to ferrying payloads between orbits which do not involve a significant change in orbit altitude. The reason for this is that round trips with the orbiting space tugs of the prior art between orbits which have significantly different altitudes involve using excessive quantities of propellant. Thus, to date, no known spacecraft have completed round trips from an orbiting platform to an orbit at a significantly different altitude than the platform and return. In the prior art, the excessive quantity of propellant used for performing the round trip with a space tug from the orbiting platform to, for example, the significantly lower orbit into which the earth launcher injects its payload, and return to the orbiting platform has prevented any significant launch cost reduction from being realized by using the orbiting space tug. The present invention overcomes the problems of the conventional approach as will be described in greater detail below.
In accordance with a first method of the present invention a method for operating a spacecraft is provided. The method comprises the steps of placing a spacecraft in a second orbit, changing orbital altitudes of the spacecraft to transfer the spacecraft from a first orbit to a second orbit, changing an orbital plane of the spacecraft, and changing orbital altitudes of the spacecraft to return the spacecraft from the second orbit to the first orbit. The second orbit is at a different altitude than the first orbit of the spacecraft. The change in orbital plane is from an initial orbital plane to a different orbital plane. The orbital altitude change to place the spacecraft in the second orbit and the orbital plane change are performed at substantially the same time.
In accordance with a second method of the present invention, a method for operating the spacecraft is provided. The method comprises the steps of providing the spacecraft with a maneuvering system, and operating the maneuvering system to perform a round trip maneuver with the spacecraft. The maneuvering system is used to maneuver the spacecraft in orbit. The spacecraft is placed in a first orbit. The spacecraft is maneuvered with the maneuvering system from an original position of the spacecraft in the first orbit to a second orbit. The second orbit has an altitude different than the first orbit. The spacecraft is returned with the maneuvering system from the second orbit to the original position in the first orbit. The maneuvering system is operated to substantially simultaneously change an orbital plane and orbital altitude of the spacecraft for completing the round trip maneuver with minimum energy expenditure from the maneuvering system.
In accordance with the third method of the present invention, a method for transporting a payload to a spacecraft is provided. The method comprises the steps of placing the payload in a first orbit, providing an orbital maneuvering spacecraft, operating a maneuvering thruster of the orbital maneuvering spacecraft, capturing the payload with the orbital maneuvering spacecraft, and transferring the payload from the orbital maneuvering system to the spacecraft. The spacecraft is placed in a second orbit substantially higher than the first orbit. The orbital maneuvering spacecraft is disposed in the second orbit in proximity to the spacecraft. The maneuvering thruster of the orbital maneuvering spacecraft is operated to substantially simultaneously lower an orbital altitude and change an orbital plane of the orbital maneuvering spacecraft for transferring the orbital maneuvering spacecraft from the second orbit into the first orbit. The maneuvering thruster of the orbital maneuvering spacecraft is further operated to raise orbital altitude of the orbital maneuvering spacecraft and return the orbital maneuvering spacecraft to the second orbit within sufficient proximity of the spacecraft to transfer the payload from the orbital maneuvering spacecraft to the spacecraft.
In accordance with an embodiment of the present invention, a spacecraft is provided. The spacecraft comprises a spacecraft bus, a maneuvering thruster system, and a controller. The maneuvering thruster system is mounted on the spacecraft bus. The controller is mounted on the spacecraft bus. The controller is operably connected to the maneuvering thruster system for maneuvering the spacecraft. The controller operates the thrusters for changing the spacecraft""s orbital altitude and for changing an orbital plane of the spacecraft from an initial orbit of the spacecraft. The orbital plane and orbital altitude are changed by the controller substantially simultaneously.